Posterior and intermediate eye diseases that require ocular drug delivery to prevent blindness include uveitis, bacterial and fungal endophthalmitis, age-related macular degeneration, viral retinitis, and diabetic retinopathy, among others. For example, the reported incidence of posterior uveitis is more than 100,000 people in the United States. If left untreated, uveitis leads to blindness. It is responsible for about 10 percent of all visual impairment in the U.S. and is the third leading cause of blindness worldwide.
Treatments of intermediate and posterior uveitis are complicated by the inaccessibility of the posterior eye to topically applied medications. Current therapy for intermediate and posterior uveitis requires repeated periocular injections and/or high-dose systemic therapy with corticosteroids. Injections are usually preferred to systemic drug administration because the blood/retinal barrier impedes the passage of most drugs from the systemically circulating blood to the interior of the eye. Therefore large systemic doses are needed to treat intermediate and posterior uveitis, which often result in systemic toxicities including immunosuppression, adrenal suppression, ulcerogenesis, fluid and electrolyte imbalances, fat redistribution and psychological disorders.
Endophthalmitis affects approximately 10,000 people in the United States each year. Endophthalmitis is typically caused by gram-positive bacteria after ocular surgery or trauma, but it can also be fungal or viral in nature. The current method of treating endophthalmitis is direct injection of antimicrobials into the vitreous. Intravitreal injections are necessary because periocular injections and systemic administration do not deliver efficacious amounts of antibiotics to the target sites in the eye. Age-related macular degeneration (AMD) is the leading cause of irreversible loss of central vision in patients over the age of 50. AMD affects more than 15 million people worldwide.
Treatments of posterior eye diseases require intravitreal and periocular injections or systemic drug administration. Systemic administration is usually not preferred because of the resulting systemic toxicity as discussed above. While intravitreal and periocular injections are preferable to systemic administration, the half-life of most injected compounds in the vitreous is relatively short, usually on the scale of just a few hours. Therefore, intravitreal injections require frequent administration. The repeated injections can cause pain, discomfort, intraocular pressure increases, intraocular bleeding, increased chances for infection, and the possibility of retinal detachment. The major complication of periocular injections is accidental perforation of the globe, which causes pain, retinal detachment, ocular hypertension, and intraocular hemorrhage. Other possible complications of periocular injections include pain, central retinal artery/vein occlusion, and intraocular pressure increases. Therefore, these methods of ocular drug delivery into the posterior of the eye have significant limitations and major drawbacks. In addition, injections are very poorly accepted by patients. These methods also involve high healthcare cost due to the involvement of skilled and experienced physicians to perform the injections.
Ocular iontophoresis is a noninvasive technique used to deliver compounds of interest into the interior of a patient's eye. In practice, two iontophoretic electrodes are used in order to complete an electrical circuit. In traditional, transscleral iontophoresis, at least one of the electrodes is considered to be an active iontophoretic electrode, while the other may be considered as a return, inactive, or indifferent electrode. The active electrode is typically placed on an eye surface, and the return electrode is typically placed remote from the eye, for example on the earlobe. The compound of interest is transported at the active electrode across the tissue when a current is applied to the electrodes. Compound transport may occur as a result of a direct electrical field effect (e.g., electrophoresis), an indirect electrical field effect (e.g., electroosmosis), electrically induced pore or transport pathway formation (electroporation), or a combination of any of the foregoing.
One potential problem with present ocular iontophoretic methods and devices concerns the actual delivery, or rather, the non-delivery of the drug into the eye tissue. Because the return electrode is located remote from the eye, various conductive pathways may be formed. Such divergence of the electric current will decrease the efficiency of drug delivery to the target sites in the eye, and as a result, much of the drug may be delivered into the tissues surrounding the eye rather than into the eye per se.
Additionally, despite its apparent advantages, iontophoresis is really just a method of limiting the invasiveness of drug delivery into the eye's interior. Once inside the eye, the pharmacokinetics of water soluble compounds are identical to those following intravitreal injections i.e. their half-lives are on the order of a few hours. Therefore, in many cases, traditional iontophoresis must be repeated as frequently as intravitreal injections, leading to patient inconvenience, increased costs, and increased possibility of untoward effects caused by the iontophoretic treatment itself.
The problem of patient compliance may be compounded by the need to receive daily treatment in a medical facility with high healthcare costs and limited resources and practitioners for treating retinal diseases. Existing ocular iontophoresis systems are not patent-friendly, require multiple parts and assembly to practice, and include either clumsy or complicated procedures. As such, they require the involvement of experienced healthcare professionals to perform the treatments. Paraprofessional and/or in-home self administration use of such devices are precluded by the technical complexity of many existing iontophoretic devices, as well as the costs of expensive dose-controlling equipment. Individuals have a greater tendency to deviate from a medication regimen when required to leave home for medical treatment, particularly when such treatment is frequent.